1. Field of the Invention
The present invention relates to a work feeder provided in a vertical machine tool with a spindle, such as a vertical lathe with a movable main spindle.
The vertical machine tool has a headstock for rotatably supporting a spindle having an axis in a vertical direction or in a direction slanted at a predetermined angle relative to the vertical direction. The headstock is moved at least in an axial direction (Z-axis direction) of the above-described main spindle and a direction (X-axis direction) perpendicular to the axial direction of the main spindle. A work (namely, workpiece) is detachably held by a chuck provided at a lower end of the above-described spindle.
2. Description of the Related Art
In the lathe among machine tools, a chuck is mounted at a tip end of a main spindle, and a work is clamped by the chuck for rotation. Among lathes, a vertical lathe having a main spindle axis directed up and down (in the vertical direction) is known in addition to a kind of vertical lathe having a main spindle directed horizontally.
For example, Japanese Patent Application Laid-Open Nos. Sho 62-166902 and 62-199301 disclose a vertical type, composite numerically controlled lathe (vertical NC lathe) with a work index table.
This lathe is of the main spindle fixed type. For this reason, it is necessary to provide a material mover (hydraulic cylinder, or the like) for moving vertically the material for loading and unloading the material relative to a power chuck, and a hydraulic cylinder for reciprocating the index table. As a result, the lathe becomes complicated in structure.
In contrast, Examined Japanese Patent Publication No. Hei 2-46321 filed by the present applicant, discloses an improved machine tool in which a main spindle is moved so that a chuck provided at a lower end of the main spindle may directly clamp a work to effect the machining.
In this machine tool, the material mover, the hydraulic cylinder, and the like, are dispensed with, thereby simplifying the structure. A work feeder (automatic workpiece feeding device) for automatically feeding works is provided.
In some cases, a non-machined work, such as a raw work before machining, intrinsically suffers from non-uniformity in dimension (for example, a diameter dimension, an axial length dimension).
Even with such non-uniformity, in the vertical machine tool with the movable main spindle, it is necessary to avoid excessive depression of the chuck for clamping the non-machined work to cause an extra load toward the machine tool (in particular, on the main spindle portion, such as bearings for rotatably supporting the main spindle). Also, in the machine tool, it is necessary to positively bring the non-machined work into intimate contact with the chuck and to hold the work with high precision.
However, in the machine tool disclosed in Examined Japanese Patent Publication No. Hei 2-46321, any consideration of the non-uniformity of the non-machined work is not paid. Accordingly, if the non-machined work suffers from a non-uniformity in dimension, it is difficult to perform the operation of holding the non-machined work in intimate contact with the chuck with high precision.
For this reason, conventionally, in the case where the non-machined work is clamped by a chuck, in order to bring the non-machined work into intimate contact with claws of the chuck, in some cases, it is necessary to independently provide a pusher specialized in pushing in a tool rest or a tailstock of the lathe. In this case, since it takes a long time to bring the work into intimate contact with the chuck by the pusher, it also takes a long time to exchange works, which creates the non-working time of the machine tool.
In addition, in order to positively receive the non-machined work from the work feeder to the chuck and to clamp the non-machined work, an operator must always lay the non-machined work within a grip range of the chuck. For this reason, the operator must lay the non-machined works so that centers of the non-machined works are substantially identical with each other on the work feeder. The workability is inferior.
Also, if a large non-uniformity exceeding the stroke for gripping of the claws of the chuck occurs in a position on a pallet where the operator lays the non-machined works, it is difficult to grip the non-machined work by the chuck. Also, there is a fear that the claws and the non-machined work would collide with each other.